A more efficient method to take asphalt pavement layer temperatures is the subject of a new standard developed by Subcommittee E17.41 on Pavement Management. The document, D 7228, Test Method for Prediction of Asphalt-Bound Pavement Layer Temperatures, details surface temperature measurement and is based on temperature relationships in the Federal Highway Administration’s Long Term Pavement Performance Seasonal Monitoring Program.

The new D 7228 BELLS procedure, an acronym of the names of the people who developed the method  Susanna Baltzer, Hans Ertman-Larsen, Erland Lukanen, and Richard Stubstad  provides an alternative to previous means used to gain pavement temperatures. Richard N. Stubstad, principal engineer with Applied Research Associates, said, “It is time-consuming, difficult and generally inaccurate to obtain pavement layer temperatures using temperature probes and drilled holes in the pavement. This method allows one to obtain a more accurate average temperature at depth, usually mid-depth, of a pavement than can be obtained by other means.”

The D 7228 method calls for an infrared thermometer, either mounted or hand-held, or a surface contact thermometer, along with recorded temperature measurements, time of day, average one-day temperature, and pavement depth. The collected information then goes into a regression formula to predict the temperature within the asphalt pavement at depth.

“BELLS makes the process much quicker and allows it to be more easily incorporated into computer analysis programs,” said Erland Lukanen, pavement preservation engineer, Minnesota Department of Transportation. The method also provides a greater amount of temperature data because there is a temperature for each test point, and it includes the ability to record temperature variations between test points.

Stubstad notes that the most critical part of the BELLS equation is the infrared surface temperature measurement: “Any error in this measurement will result in an almost equally incorrect at-depth temperature value.” The standard notes that the temperature measurement device should be calibrated according to manufacturer recommendations.

Subcommittee E17.41, a part of Committee E17 on Pavement-Vehicle Systems, welcomes data from studies independent of the FHWA long-term pavement study. Additional participation, particularly from users of E17.41 standards, is also encouraged. //